If you have an attic, you know just how hot it can get in the summer — temperatures in excess of 150°F are fairly common. (It can get even worse if your roof has dark-colored shingles.) Having a massive volume of air at 150°F just above your living spaces can seriously increase your cooling bills in the summer time. There are several steps you can take you reduce your cooling bills — one of the most cost-effective is to add thermostat-controlled fans to remove that hot air from your attic.
We keep the thermostats on our attic fans set at 100°F to keep temperatures down. The electricity we use to keep the fans running is more than offset by the electricity we don't use to run the air conditioner. When selecting attics fans, always consider the volume of your attic. The general goal is to have all of the air in your attic replaced every minute until the attic temperature approachs the temperature of the outside air. During the day, when the sun is shining, there is so much energy hitting your roof — especially if it is dark-colored — that your attic fans will run all day long without a pause. An average attic fan for sale at Lowe's will suck out about 1,500 cubic feet per minute, which may sound like a lot but really isn't all that much. (We have four 1,500-cubic-foot-per-minute attic fans in our attic, which sounds like the house is about to take flight when all four turn on at once.)
A solar-powered attic fan may seem like a great idea because the fan runs essentially for free. The problem, however, is that the typical solar fan will only suck out 800 cubic feet per minute and will only run while the sun is shining. Some people have reported that the solar panels on solar attic fans burn out after a few years, as well — does anyone have experience with these?
One last note: If you decide to add some attics fans, remember that working on your roof can be incredibly dangerous. Even more dangerous can be working in the attic in the summer — it is very easy to get heatstroke working in the attic. Be warned!
Wow! It's hot out! As earnest energy watchers, what can we do to cool off that doesn't drive up the utility bills? Take a cold shower! Take it from me, taking a brief, cold shower in the summer can really change your perspective on the heat.
Keeping showers brief keeps humidity out of the air — much of the power consumed by your air conditioning is used to remove the humidity from the air.
Keeping showers cold also avoids using hot water, which saves you money first because you don't have to heat that water and second because the waste heat from your shower does not have to be removed by your air conditioner.
Give it a try!
If you still have halogen torchiere light fixtures — Amazon still sells them
— throw them out! But, you say, halogen torchieres put out a hell of a lot of light and don't cost very much. Why throw them out?
Well, first, halogen lamps get hot, hot enough to start fires if the lamp gets knocked over. (Halogen light bulbs are every bit as inefficient as incandescent light bulbs, after all.) All of this heat makes your air conditioner work much harder than it needs to, which is an important factor in the summertime. How much heat? So much heat that you can actually buy an oven powered by halogen light bulbs.
And, possibly most important, halogen torchieres use 300-watt light bulbs. 300 watts! There is no way you could possibly need that much light at any one point in any room of your house — wherever possible, use lighting appropriate to what you actually need at the time.
A kind reader, Guy Kuo, recently proposed a new way to keep your home cool this summer. Here is the relevant part:
Once air conditioning season arrives, seal the house. Do not open the windows at night to cool the house. Set the air conditioning system to cool the house below normal at night and allow the house's thermal capacity coast through most of the hot day without air conditioning.
This is contrary to almost every single website about saving energy that I have read. Normally, one sees advice saying to open your windows at night to let night air cool the house. That seems perfectly logical. Night air is cooler and costs nothing to to use. Sadly, that common sense strategy is not always right. For someone in a well insulated home like we have, opening the windows at night ended up increasing our total air conditioning usage. Why?- Water vapor enters the house along with the night air. The increased humidity decreases comfort and drops air conditioning efficiency the next day because you have to spend energy removing water from the house before you get net cooling from the air conditoner. If one opens windows and lets cool air in at night, one also allows a great deal of humidity into the house. That water vapor is not only in the air, but it is absorbed into carpeting and upholstery. When the next day's air conditioning begins, a major portion of the air conditioner's energy usage is spent removing all the water vapor that was introduced overnight into the house. Worse yet, increased indoor humidity means things feel hotter at the same temperature than at a lower humidity. That "common sense" night time window opening ends up increasing how long you need to run the air conditioner during the day.
- An air conditioner compressor is more efficient removing heat when it is cooler outdoors. Running the air conditioner while the outdoor air is cool, allows the heat pump to be more efficient because it does not have to work against as large a temperature gradient as during the hot mid-day. Shifting air conditioning to the night also moves that load off-peak. In some localities, off peak electricity is also cheaper.
- Having a cooler house at night makes sleeping a lot easier. Even with windows open, we could never get truly comfortable. Outdoor air was cooler, but there was always a mugginess and things never got cool enough until past midnight.
Air conditioning at night instead of during the day is worth trying. Your home must well insulated and with shades closed. Our experience has been that cooling the house to about 67 degrees at 10 PM, means we can very comfortably coast through a 90 degree day without hearing the air conditioner come on until 7 PM. It was truly amazing the first week we tried the strategy. A programmable thermostat makes it easy to dive the temp at night and let things coast during the day.
The first day on this regimen will require a longer air conditioner run to initially remove water vapor, but thereafter the house will remain a low humidity, cool refuge all 24 hours. Our home remains very comfortable throughout 24 hours and we only use about 1.5 hours of compressor time total. As a result of adopting night time air conditioning, our electric bill for summer vs winter is at most 5% higher and I am always comfortable.
I am seriously considering trying this myself, although I am concerned about solar gain through the windows on the south side of our house. I am starting to think that window film project is coming up in my near future.
Can I persuade anyone else to try this and report on your results?
Our weather for May 2009 was pretty much the same as the weather for May 2008, although it was a bit rainier as I recall. Electricity and water costs were up and natural gas costs were down. The big difference, I believe, is that we had five people living under our roof this year but we had three people living here last year.
Georgia is no longer suffering from a drought, so we are now legally allowed to water our yards. After much work with the sprinkler system, we turned it on — and managed to get through 7,500 gallons of water, at a cost of $25, in just 20 or so days. Although I seriously need to adjust the settings, I do have to say that the yard looks great.
Our middle daughter moved out last week and our oldest daughter is moving out next week, so we can hope for a reduction in our overall utility bills comparable to what we had in May 2008. I do know that when the weather started to seriously warm up in mid-May, the attic exhaust fans we installed last year started coming on during the middle of the day. Between this and our aggressive approach to setting the thermostat, I am hopeful that we will be able to show lower BTUs per square foot, year-over-year, next month. Tune back in next month find out!
May 2009 Data
| Electricity, in kWh | Cost / Unit | Gas, in Therms | Cost / Unit | Water, in CCF | Cost / Unit | BTUs / Ft2 |
| 869 | $.097 | 41 | $1.56 | 20 | $2.85 | 2,020 |
Always pay attention to the humidity — it can have a dramatic effect on your cooling bills.
Sometimes you step out the door and you find out that it is cooler outside than it is inside. This can be fairly frustrating. After all the trouble and expense you have gone through to ensure that you have properly insulated your home and weatherstripped all of your doors and windows, now you are keeping the heat in! You will be tempted to open all of your doors and windows to let the heat out. Depending on the humidity outside, this may or may not be a good idea.
A lot of what your air conditioner does is remove the humidity from the air. Humid air just feels hotter than air that has had the humidity removed — this is why Miami feels hotter than Phoenix when they are actually the same temperature. It takes a lot of energy to de-humidify the air in your house, and there is actually a lot of air inside your house. Before you open the doors and windows, always consider not just the difference in temperature but also the difference in humidity.